1. Field of the Invention
The present invention relates to electronically energized light emitters and particularly to control circuits for generating trigger pulses for application to gaseous discharge tube devices. More specifically, this invention is directed to enhancement of the noticeability of warning devices such as, for example, those which employ repetitively energized flash tubes. Accordingly, the general objects of the present invention are to provide novel and improved apparatus and methods of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention has been found to be particularly well suited for use with and/or as a warning device. Warning devices employing Xenon flash tubes are well known in the art and find application on emergency vehicles, aircraft and in other installations where it is considered necessary or desirable to attract attention by means of the generation of intermittent bursts of energy in the visible range of the frequency spectrum. It is generally accepted that electronic flash tubes, such as the aforementioned Xenon tubes, are more readily visible than previous mechanically energized oscillating and rotating beacon type devices. Nevertheless, for some time it has been desired to enhance the attention gathering properties of warning lights employing flash tubes.
For a disclosure of a typical prior art technique for the periodic energization of devices such as gaseous discharge tubes employed as light generators, reference may be had to U.S. Pat. No. 3,515,973 which is assigned to the assignee of the present invention. Power supplies of the type exemplified by U.S. Pat. No. 3,515,973 generate, from a low voltage source, a high voltage which is applied to a capacitive discharge circuit across which the flash tube is connected. The power supply circuits further generate trigger pulses which control the discharge of energy from such capacitive discharge circuits through the flash tube when it is desired to produce a light pulse. The discharge time; i.e., the length of the light pulse produced; is comparatively short and thus the visibility thereof is somewhat limited in spite of the fact that the intensity of the light generated is extremely high. Additionally, with prior art power supplies for flash tubes, the duty cycle is very low. That is, the dwell time between generation of successive trigger pulses constitutes the major portion of the operational cycle.
It has been long recognized, for example as observed in U.S. Pat. No. 3,430,102, that the visibility of a warning light could be enhanced by causing a lamp to "flash" twice in rapid succession. If a pair of flashes in rapid succession were to be produced, the lamp could appear, as a consequence of the retention characteristics of the human eye, to provide a single flash of long duration. Such a "lengthened" output pulse would, of course, have enhanced visibility in comparison to a single light flash of shorter duration.
It is also well known that a discernable double flash enhances visibility. This is particularly true in the case of moving objects where tests have shown that an observer may fix the position of such objects much more readily when two flashes occur in rapid succession than with a single flash followed by the customary delay until a succeeding flash is produced.
If a warning light is to be a commercially viable product, it is necessary that it be characterized by control circuitry which is designed to operate reliably in a rather harsh environment while simultaneously being economical to produce. There has not previously been available an economic and reliable circuit for producing trigger pulse pairs with adjustable timing for use in the firing of gaseous discharge tubes, and particularly Xenon flash tubes, to thereby permit generation of either an apparent long duration flash, a pair of discernable flashes closely spaced in time or a pattern of "double" flashes.
In addition to enhancement of the visibility of warning lights, it is in many instances considered desirable to further augment the attention gathering capability of warning light devices by some auxiliary means. Thus, by way of example, the requirements of the Occupational Safety and Health Act of 1970 have required that devices such as electric trucks for use in factory areas be provided with both visible warning beacons and some form of noise maker which is energized when the vehicle is placed in reverse gear. At the present time separate power supply circuits are employed for energization of the warning beacon and the sound generator. Such use of separate power supplies, of course, increases cost and reduces the reliability of the apparatus. It would thus be desirable to employ the same power supply used to intermittently energize a flash tube type warning light to simultaneously intermittently energize a suitable noise maker to thereby produce pulses of light and sound.